function seq() {
    if(!seq.instance){
        seq.instance = this
        var i=0;
        this.say = function(){
            return ++i;
        }
    }
    return seq.instance
}

var seq1= new seq()
console.log(seq1.say())
console.log(seq1.say())
console.log(seq1.say())

var seq2= new seq()
console.log(seq2.say())


console.log('1111111111',seq.prototype)
console.log('4444444444',seq.prototype.constructor)
console.log('2222222222',seq1.__proto__)
console.log('3333333333',seq1.__proto__.constructor)

console.log(seq.prototype == seq1.__proto__)
console.log(seq.prototype === seq1.__proto__)
console.log(seq.prototype.constructor === seq1.__proto__.constructor)

